(1) Field of the Invention
This invention relates to an improved radiation-sensitive polymer composition which can give highly heat-resistant relief structures.
(2) Description of the Prior Art
Photosensitive polymer compositions, used to form heat-resistant relief patterns, are known as shown in the following patent references:
(a) U.S. Pat. No. 3,623,870 to Curran et al issued on Nov. 30, 1971, PA1 (b) U.S. Pat. No. 3,957,512 to Kleeberg et al issued on May 18, 1976, PA1 (c) U.S. Pat. No. 4,040,831 to Rubner et al issued on Aug. 9, 1977, and PA1 (d) U.S. Pat. No. 4,243,743 to Hiramoto et al issued on Jan. 6, 1981.
According to each of these conventional techniques, a varnish formed by dissolving a photosensitive polymer composition in an appropriate organic solvent is coated and dried on a substrate, and the coating is irradiated with ultraviolet rays through an appropriate photomask and is then subjected to developing and rinsing treatments to obtain an intended relief pattern.
A patterned coating of a polyimide precursor is subjected to an appropriate heat treatment to be thereby converted into a polyimide coating exhibiting heat resistance.
Patterning of these known compositions can be accomplished directly by irradiation with light. However, the composition disclosed in the patent reference (a) has poor stability. Thus, the composition should be used just after mixing of a polyamide acid with dichromic acid, and hence, industrial utilization of this composition is considerably limited. Moreover, since inorganic ions are present in the patterned film formed from this composition, the patterned film cannot be used in the field of semiconductors where the reliability is seriously influenced by the presence of inorganic ions.
In each of the compositions disclosed in the patent references (b) and (c), the constituent polymer is mainly formed by reacting a compound having a photosensitive group and a dibasic acid chloride group with a diamine, and the steps of forming this polymer are complicated. Furthermore, since the chlorine ion generated by dehydrochlorination is left in the film, there is a risk of having bad influences on the reliability in the field of semiconductors.
The composition disclosed in the patent reference (d) is improved over the above-mentioned compositions in that it has an excellent sensitivity to light or radiation, and is obtained according to a simple method comprising mixing a polymer having poly (amic acid) as a main constituent with an amine compound having an olefinic double bond and an amino group or quaternary salt thereof. However, this composition has a limited commercial value because the light exposure time necessary for obtaining a good relief pattern is too long and therefore, the composition is not applicable to a modern process.